This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-006452, filed Jan. 15, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor light emitting device such as a light emitting diode (LED) and a semiconductor laser (LD) and more particularly to a semiconductor light emitting device whose light pickup surface is formed in a form of rough surface and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, a light emitting portion of a high luminance light emission diode has a double-hetero structure or the like formed on a semiconductor substrate, and a current diffusion layer is formed on the light emitting portion. When the light emitting diode is packaged with resin, the upper portion of the current diffusion layer is covered with a transparent resin layer to protect the semiconductor device.
With this structure, a critical angle between the current diffusion layer (refractivity: 3.1 to 3.5) and the transparent resin layer (refractivity: about 1.5) is 25 to 29 degrees and a light having an incident angle larger than the critical angle is subject to total reflection, so that the pickup rate of light emitted from the light emitting device remarkably decreases. As a result, a pickup efficiency of the generated light remains generally about 20%.
In order to improve the light pickup efficiency, there is a technique of making the surface of the current diffusion layer rough. However, generally, the main surface of the semiconductor substrate is in a (100) plane or in a plane of (100)xc2x1several degrees off. Thus, a surface of a semiconductor layer grown on the main surface of the semiconductor substrate is also in the (100) plane or a plane of (100)xc2x1several degrees off. It is difficult to make the plane of (100) or (100)xc2x1several degrees off rough.
Hence, conventionally, a light emitting diode packaged with a resin has such a problem that on a boundary between the uppermost layer and the transparent resin layer of a multi-layer semiconductor film containing a light emission layer, a light entered obliquely into the boundary is subject to total reflection, so that the light pickup efficiency is decreased. Further, this problem is not restricted to the light emitting diode, and is also applicable to a surface-light-emission type semiconductor laser.
According to a first aspect of the present invention, there is provided a semiconductor light emitting device comprising a substrate; and a multi-layer semiconductor film formed on the substrate, the multi-layer semiconductor film including a plurality of semiconductor layers overlaid on the substrate, the semiconductor layers having a light emission layer for emitting a light, wherein the light is picked up at a first side of the multi-layer semiconductor film, which is a side opposite to the substrate, wherein a pattern having a light pickup surface is formed on a light emitting portion of the multi-layer semiconductor film, the light pickup surface is in a (111) plane or a plane in the vicinity of the (111) plane, and an unevenness is formed on the light pickup surface.
According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor light emitting device according to the first aspect, comprising blading a light pickup surface formed of the (100) plane to expose the (111) plane or the plane in the vicinity of the (111) plane; and carrying out a rough surface processing on the (111) plane exposed or the crystal plane exposed in the vicinity of the (111) plane to form the unevenness.
According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor light emitting device according to the first aspect, comprising forming a line-and-space mask on a light pickup surface of the (100) plane; reactive ion etching the light pickup surface into a tapered form using the mask to expose the (111) plane; and carrying out rough surface processing on the (111) plane exposed to form the unevenness.